The Italian has also ruled out a move for Dutch playmaker Wesley Sneijder, who looks set to leave Serie A side Inter.
As exclusively reported by Goal.com in August, City saw a move for De Rossi in the summer transfer window fall though, with the Roma captain eventually opting to stay at the Serie A club and Mancini has admitted that the episode has spelled the end for his pursuit of the Italian midfielder.
"We tried to get De Rossi last summer but didn't succeed and now we're not interested," Mancini told Sky Sport Italia. "At the moment we don't need De Rossi, I think he'll stay at Roma."
The City boss has also denied any interest in Inter midfielder Sneijder. The Dutch international, who helped the Nerazzurri to a historic treble in 2010, seems certain to leave the club following a contract dispute, but Mancini has quashed reports that he may be heading to Manchester City.
"Sneijder is a very good player but we have two players in [Samir] Nasri and [David] Silva who have the same skills as Sneijder," he explained. "So Sneijder can't be helpful for us."